U.S. patent application number 16/418000 was filed with the patent office on 2020-06-11 for system and method of controlling operation of fuel cell.
The applicant listed for this patent is Hyundai Motor Company Kia Motors Corporation. Invention is credited to Hyun Suk Choo, Dae Jong Kim.
Application Number | 20200185735 16/418000 |
Document ID | / |
Family ID | 70971114 |
Filed Date | 2020-06-11 |
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United States Patent
Application |
20200185735 |
Kind Code |
A1 |
Kim; Dae Jong ; et
al. |
June 11, 2020 |
SYSTEM AND METHOD OF CONTROLLING OPERATION OF FUEL CELL
Abstract
An operation control system of a fuel cell is provided. The
system includes a fuel cell stack and a motor connected to the fuel
cell stack via a main bus end to receive power. A booster is
disposed between a load and the fuel cell stack of the main bus end
to adjust an output voltage of the fuel cell stack. A high-voltage
battery is connected between a load and the booster of the main bus
end and a voltage sensor is connected between the booster and the
fuel cell stack of the main bus end to measure an output voltage of
the fuel cell stack.
Inventors: |
Kim; Dae Jong; (Yongin,
KR) ; Choo; Hyun Suk; (Seongnam, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Hyundai Motor Company
Kia Motors Corporation |
Seoul
Seoul |
|
KR
KR |
|
|
Family ID: |
70971114 |
Appl. No.: |
16/418000 |
Filed: |
May 21, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01M 8/0494 20130101;
H01M 2250/20 20130101; H01M 8/0488 20130101; H01M 8/0491 20130101;
B60L 50/75 20190201; B60L 3/0053 20130101; H01M 16/006 20130101;
B60L 58/40 20190201; B60L 58/32 20190201; H01M 8/04559
20130101 |
International
Class: |
H01M 8/04858 20060101
H01M008/04858; H01M 8/04537 20060101 H01M008/04537; H01M 8/04828
20060101 H01M008/04828; H01M 16/00 20060101 H01M016/00; B60L 50/75
20060101 B60L050/75 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 6, 2018 |
KR |
10-2018-0156327 |
Claims
1. An operation control system of a fuel cell, comprising: a fuel
cell stack; a motor connected to the fuel cell stack via a main bus
end to receive power, a booster disposed between a load and the
fuel cell stack of the main bus end to adjust an output voltage of
the fuel cell stack; a high-voltage battery connected between a
load and the booster of the main bus end; a voltage sensor
connected between the booster and the fuel cell stack of the main
bus end to measure an output voltage of the fuel cell stack; and a
voltage controller configured to set an upper or lower voltage
limit of the fud cell stack based on a state of the fuel cell stack
or the high-voltage battery and to operate the booster to maintain
the output voltage of the fuel cell stack, measured by the voltage
sensor, at the set upper voltage limit or less or the set lower
voltage limit or greater.
2. The operation control system of the fuel cell of claim 1,
wherein the voltage controller is configured to operate the booster
to charge the high-voltage battery while increasing output current
of the fuel cell stack when the output voltage of the fuel cell
stack is equal to or greater than the set upper voltage limit.
3. The operation control system of the fuel cell of claim 1,
wherein the voltage controller is configured to operate the booster
to discharge the high-voltage battery while maintaining the output
voltage of the fuel cell stack when the output voltage of the fuel
cell stack is equal to or less than the set lower voltage
limit.
4. The operation control system of the fuel cell of claim 1,
wherein the voltage controller is configured to set a first voltage
and a second voltage, which arc respectively preset to a maximum
voltage and minimum voltage of an operation voltage range in which
durability of the fuel cell stack is optimized, to the upper
voltage limit and the lower voltage limit, respectively, in a state
in which the fuel cell stack generates power normally.
5. The operation control system of the fuel cell of claim 4,
wherein the voltage controller is configured to set the lower
voltage limit to a third voltage, which is less than the second
voltage and is preset to an allowable minimum voltage of the fuel
cell stack, when a temperature of the fuel cell stack is estimated
to a preset temperature or less.
6. The operation control system of the fuel cell of claim 4,
wherein when a sum of power output from the fuel cell stack and
dischargeable power of the high-voltage battery is less than power
required by the motor in a state in which the output voltage is the
second voltage, the voltage controller is configured to set the
lower voltage limit to a third voltage, which is less than the
second voltage and is preset to an allowable minimum voltage of the
fuel cell stack.
7. The operation control system of the fuel cell of claim 1,
wherein when the fuel cell stack enters a fuel cell (FC) stop mode,
the voltage controller is configured to set a first voltage, which
is preset to a maximum voltage of a voltage range in which
durability of the fuel cell stack is optimized, to the upper
voltage limit, and set a third voltage, which is preset to an
allowable minimum voltage of the fuel cell stack, to the lower
voltage limit.
8. The operation control system of the fuel cell of claim 7,
wherein the voltage controller is configured to stop adjustment
control of a voltage of the fuel cell stack using the booster when
the voltage of the fuel cell stack is reduced to the third voltage
or less.
9. The operation control system of tire fuel cell of claim 8,
further comprising: a relay disposed between the booster and the
fuel cell stack of tire main bus end; and a relay controller
configured to turn the relay on or off, wherein the relay
controller is configured to block the relay when the fuel cell
stack enters the FC stop mode and the voltage of the fuel cell
stack is reduced to the third voltage or less.
10. The operation control system of the fuel cell of claim 1,
wherein when the fuel cell stack is released from a fuel cell (FC)
stop mode, the voltage controller is configured to set a fourth
voltage, which is preset to a maximum voltage for durability of the
fuel cell stack, to the upper voltage limit.
11. The operation control system of the fuel cell of claim 1,
wherein maximum dischargeable power of the high-voltage battery is
about 70% or greater of maximum power to be consumed by the
motor.
12. The operation control system of the fuel cell of claim 1,
wherein maximum chargeable power of the high-voltage battery is
about 70% or greater of maximum power to be output from the fuel
cell stack.
13. An operation control method of a fuel cell, comprising:
determining, by a controller, a state of a fuel cell stack or a
high-voltage battery; setting, by the controller, an upper or lower
voltage limit of the fuel cell stack based on the determined stale
of the fuel cell stack or the high-voltage battery; and operating,
by the controller, a booster disposed at a main bus end for
connection between the fuel cell stack and a motor to maintain an
output voltage of the fuel cell stack, at the set upper voltage
limit or less or the set lower voltage limit or greater.
14. The method of claim 13, wherein in response to determining that
the fuel cell stack is in a state in which power is normally
generated, lire setting of the upper voltage limit or the lower
voltage limit includes: setting, by the controller, a first voltage
and a second voltage, which arc respectively preset to a maximum
voltage and a minimum voltage of an operation voltage range in
which durability of the fuel cell stack is optimized, to the upper
voltage limit and the lower voltage limit, respectively.
15. The method of claim 14, wherein in response to determining that
a temperature of the fuel cell stack is equal to or less than a
preset temperature, the setting of the upper voltage limit or the
lower voltage limit includes: setting, by the controller, the lower
voltage limit to a third voltage, which is less than the second
voltage and is preset to an allowable minimum voltage of the fuel
cell stack.
16. The method of claim 14, wherein when a sum of power output from
the fuel cell stack and dischargeable power of the high-voltage
battery is less than power required by the motor in a state in
which the output voltage is the second voltage, the setting of the
upper voltage limit or the lower voltage limit includes: setting,
by the controller, the lower voltage limit to a third voltage,
which is less than the second voltage and is preset to an allowable
minimum voltage of the fuel cell stack.
17. The method of claim 13, wherein in response to determining that
the fuel cell stack enters a fuel cell (FC) stop mode in the
determining of the state, the setting of the upper voltage limit or
the lower voltage limit includes: setting, by the controller, a
first voltage, which is preset to a maximum voltage of a voltage
range in which durability of the fuel cell stack is optimized, to
the upper voltage limit; and setting, by the controller, a third
voltage, which is preset to an allowable minimum voltage of the
fuel cell stack, to the lower voltage limit.
18. The method of claim 17, wherein the operating of the booster
includes: stopping, by the controller, adjustment of a voltage of
the fuel cell stack using the booster when the voltage of the fuel
cell stack is reduced to the third voltage or less.
19. The method of claim 13, wherein in response to determining that
the fuel cell stack is released from a fuel cell stop mode in the
determining of the state, the setting of the upper voltage limit or
the lower voltage limit includes: setting, by the controller, a
fourth voltage, which is preset to a maximum voltage for durability
of the fuel cell stack, to the upper voltage limit.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] The present application claims priority to Korean Patent
Application No. 10-2018-0156327, filed on Dec. 6, 2018, the entire
contents of which is incorporated herein for all purposes by this
reference.
BACKGROUND
1. Technical Field
[0002] The present disclosure relates to a system and method of
controlling an operation of a fuel cell, and more particularly, to
a technology for adjusting the voltage of a fuel cell stack to
enhance durability.
2. Description of the Related Art
[0003] A fuel cell converts chemical energy into electric energy
using an oxidation-reduction reaction of hydrogen and oxygen,
supplied from a hydrogen supply device and an air supply device,
respectively. The fuel cell includes a fuel cell stack that
generates electric energy, a cooling system that cools the fuel
cell stack, and the like. In other words, hydrogen is supplied to
an anode of a fuel cell stack, an oxidation reaction of hydrogen
proceeds to generate hydrogen ions (proton) and electrons in the
anode. The generated hydrogen ions and electrons are moved to the
cathode through an electrolyte membrane and a separator,
respectively. In the cathode, water is generated through an
electrochemical reaction in which the hydrogen ions and the
electrons that arc moved from the anode and oxygen in the air
participate, and electric energy is generated from the flow of the
electrons.
[0004] When a fuel cell stack is exposed to a high voltage close to
an open circuit voltage (OCV), the durability thereof is degraded
due to a problem such as damage to a catalyst within the fuel cell
stack. In general, a fuel cell-battery hybrid type device that uses
both a fuel cell and a high-voltage battery, which is charged with
power output from the fuel cell and is discharged, uses a
high-voltage battery with low capacitance due to limitations of
space, weight, and the like, and accordingly, the fuel cell
provides most of the power required by a motor. In particular, the
high-voltage battery has a maximum chargeable or dischargeable
output that has a much lower level than the maximum output of the
fuel cell, and is mainly used to supplement output when a fuel cell
vehicle accelerates or to recover regenerative brake energy when
the vehicle brakes.
[0005] Accordingly, when an upper voltage limit of the fuel cell
stack is limited, there is a limit in charging the high-voltage
battery with surplus output of the fuel cell stack, and thus there
is a limit in controlling the upper voltage limit of the fuel cell
stack. In addition, when the upper voltage limit of the fuel cell
stack is limited, there is a limit in an output of the high-voltage
battery that assists the output of the fuel cell, and thus there is
a limit in controlling the lower voltage limit of the fuel cell
stack. In other words it may thus he difficult to adjust the
operation voltage of the fuel cell slack, and thus there is a
problem in terms of a high frequency at which the fuel cell stack
is exposed to a high voltage. Therefore, research and development
is being conducted regarding a fuel cell-battery hybrid type device
having a high-voltage battery with high capacitance for a
commercial vehicle such as a bus a truck, or a train, which
requires high durability of a fuel cell stack and has a low limit
in space, weight, or the like of a high-voltage battery, compared
with a general passenger vehicle.
[0006] The matters disclosed in this section is merely for
enhancement of understanding of the general background of the
invention and should not be taken as an acknowledgment or any form
of suggestion that the matters form the related art already known
to a person skilled in the art.
SUMMARY
[0007] An object of the present disclosure is to provide a system
and method of controlling an operation of a fuel cell, for
preventing an operation voltage of a fuel cell from being exposed
to a high voltage close to an open circuit voltage (OCV) using a
high-voltage battery with high capacitance.
[0008] According to an exemplary embodiment of the present
disclosure, an operation control system of a fuel cell may include
a fuel cell stack, a motor connected to the fuel cell stack via a
main bus end to receive power, a booster disposed between a load
and the fuel cell stack of the main bus end to adjust an output
voltage of the fuel cell stack, a high-voltage battery connected
between a load and the booster of the main bus end, a voltage
sensor connected between the booster and the fuel cell stack of the
main bus end to measure an output voltage of the fuel cell stack,
and a voltage controller configured to set an upper or lower
voltage limit of the fuel cell stack based on a state of the fuel
cell stack or the high-voltage battery and to operate the booster
to maintain the output voltage of the fuel cell stack, measured by
the voltage sensor, at the set upper voltage limit or less or at
the set lower voltage limit or greater.
[0009] The voltage controller may be configured to operate the
booster to charge the high-voltage battery while increasing output
current of the fuel cell stack when the output voltage of the fuel
cell stack is equal to or greater than the set upper voltage limit.
The voltage controller may also be configured to operate the
booster to discharge the high-voltage battery while maintaining the
output voltage of the fuel cell stack when the output voltage of
the fuel cell stack is equal to or less than the set lower voltage
limit.
[0010] The voltage controller may be configured to set a first
voltage and a second voltage, which are respectively preset to a
maximum voltage and a minimum voltage of an operation voltage range
in which durability of the fuel cell stack is optimized, to the
upper voltage limit and the lower voltage limit, respectively, in a
state in which the fuel cell stack generates power normally.
Additionally, the voltage controller may be configured to set the
lower voltage limit to a third voltage, which is less than the
second voltage and is preset to an allowable minimum voltage of the
fuel cell stack, when a temperature of the fuel cell stack is
estimated to a preset temperature or less.
[0011] When a sum of power output from the fuel cell stack and
dischargeable powder of the high-voltage battery is less than power
required by the motor and when the output voltage is the second
voltage, the voltage controller may be configured to set the lower
voltage limit to a third voltage, which is less than the second
voltage and is preset to an allowable minimum voltage of the fuel
cell stack. When the fuel cell stack enters a fuel cell (FC) stop
mode, the voltage controller may be configured to set a first
voltage, which is preset to a maximum voltage of a voltage range in
which durability of the fuel cell stack is optimized, to the upper
voltage limit, and may be configured to set a third voltage, which
is preset to an allowable minimum voltage of the fuel cell stack,
to the lower voltage limit. The voltage controller may be
configured to stop adjustment of a voltage of the fuel cell stack
using the booster when the voltage of the fuel cell stack is
reduced to the third voltage or less.
[0012] The operation control system of the fuel cell may further
include a relay disposed between the booster and the fuel cell
stack of the main bus end, and a relay controller configured to
turn the relay on or off. The relay controller may further be
configured to block the relay when the fuel cell stack enters a
fuel cell (FC) stop mode and the voltage of the fuel cell stack is
reduced to the third voltage or less.
[0013] When the fuel cell stack is released from a fuel cell (FC)
stop mode, the voltage controller may be configured to set a fourth
voltage, which is preset to a maximum voltage for durability of the
fuel cell stack, to the upper voltage limit. Maximum dischargeable
power of the high-voltage battery may be about 70% or greater of
maximum power to be consumed by the motor. Maximum chargeable power
of the high-voltage battery may be about 70% or greater of maximum
power to be output from the fuel cell stack.
[0014] According to another exemplary embodiment of the present
disclosure, an operation control method of a fuel cell may include
determining a state of a fuel cell stack or a high-voltage battery,
setting an upper or lower voltage limit of the fuel cell stack
based on the determined state of the fuel cell stack or the
high-voltage battery, and operating a booster disposed at a main
bus end for connection between the fuel cell stack and a motor to
maintain an output voltage of the fuel cell stack, at the set upper
voltage limit or less or the set lower voltage limit or
greater.
[0015] In response to determining that the fuel cell stack is in a
state in which power is normally generated, the setting of the
upper voltage limit or the lower voltage limit may include setting
a first voltage and a second voltage, which are respectively preset
to a maximum voltage and a minimum voltage of an operation voltage
range in which durability of the fuel cell stack is optimized, to
the upper voltage limit and the lower voltage limit, respectively.
Additionally, in response to determining that a temperature of the
fuel cell stack is equal to or less than a preset temperature, the
setting of the upper voltage limit or the lower voltage limit may
include setting the lower voltage limit to a third voltage, which
is less than the second voltage and is preset to an allowable
minimum voltage of the fuel cell stack.
[0016] When a sum of power output from the fuel cell stack and
dischargeable power of the high-voltage battery is less than power
required by the motor in a state in which the output voltage is the
second voltage, the setting of the upper voltage limit or the lower
voltage limit may include setting the lower voltage limit to a
third voltage, which is less than the second voltage and is preset
to an allowable minimum voltage of the fuel cell stack. In response
to determining that the fuel cell stack enters a fuel cell (FC)
stop mode, the setting of the upper voltage limit or the lower
voltage limit may include setting a first voltage, which is preset
to a maximum voltage of a voltage range in which durability of the
fuel cell stack is optimized, to the upper voltage limit, and
setting a third voltage, which is preset to an allowable minimum
voltage of the fuel cell stack, to the lower voltage limit.
[0017] Further, the operation of the booster may include stopping
adjustment of a voltage of the fuel cell stack using the booster
when the voltage of the fuel cell stack is reduced to the third
voltage or less. In response to determining that the fuel cell
stack is released from an FC stop mode, the setting of the upper
voltage limit or the lower voltage limit may include setting a
fourth voltage, which is preset to a maximum voltage for durability
of the fuel cell stack, to the upper voltage limit.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] The above and other objects, features and advantages of the
present invention will be more clearly understood from the
following detailed description taken in conjunction with the
accompanying drawings, in which:
[0019] FIG. 1 is a diagram showing a performance reduction rate and
a platinum (Pt) charge quantity reduction rate depending on an
operating voltage range of a cell included in a fuel cell stack
according to an exemplary embodiment of the present disclosure;
[0020] FIG. 2 is a diagram showing the configuration of an
operation control system of a fuel cell according to an exemplary
embodiment of the present disclosure;
[0021] FIG. 3 is a diagram showing upper and lower voltage limits
corresponding to the state of a fuel cell stack or a high-voltage
battery according to an exemplary embodiment of the present
disclosure; and
[0022] FIG. 4 is a flowchart of an operation control method of a
fuel cell according to an exemplary embodiment of the present
disclosure.
DETAILED DESCRIPTION
[0023] It is understood that the term "vehicle" or "vehicular" or
other similar term as used herein is inclusive of motor vehicles in
general such as passenger automobiles including sports utility
vehicles (SUV), buses, trucks, various commercial vehicles,
watercraft including a variety of boats and ships, aircraft, and
the like, and includes hybrid vehicles, electric vehicles, plug-in
hybrid electric vehicles, hydrogen-powered vehicles and other
alternative fuel vehicles (e.g. fuels derived from resources other
titan petroleum). As referred to herein, a hybrid vehicle is a
vehicle that has two or more sources of power, for example both
gasoline-powered and electric-powered vehicles.
[0024] Although exemplary embodiment is described us using a
plurality of units to perform the exemplary process, it is
understood that the exemplary processes may also be performed by
one or plurality of modules. Additionally, it is understood that
the term controller/control unit refers to a hardware device that
includes a memory and a processor. The memory is configured to
store the modules and the processor is specifically configured to
execute said modules to perform one or more processes which are
described further below.
[0025] Furthermore, control logic of the present disclosure may be
embodied as non-transitory computer loadable media on a computer
readable medium containing executable program instructions executed
by a processor, controller/control unit or the like. Examples of
the computer readable mediums include, but arc not limited to, ROM,
RAM, compact disc (CD-ROMs, magnetic tapes, floppy disks, flash
drives, smart cards and optical data storage devices. The computer
readable recording medium can also be distributed in network
coupled computer systems so that the computer readable media is
stored and executed in a distributed fashion, e.g., by a telematics
server or a Controller Area Network (CAN).
[0026] The terminology used herein is for the purpose of describing
particular embodiments only and is not intended to be limiting of
the disclosure. As used herein, the singular forms "a", "an" and
"the" arc intended to include die plural forms as well, unless the
context clearly indicates otherwise. It will be further understood
that the terms "comprises" and/or "comprising," when used in this
specification, specify the presence of stated features, integers,
steps, operations, elements, and/or components, but do not preclude
the presence or addition of one or more other features, integers,
steps, operations, elements, components, and/or groups thereof. As
used herein, the term "and/or" includes any and all combinations of
one or more of the associated listed items.
[0027] Unless specifically stated or obvious from context, as used
herein, the term "about" is understood as within a range of normal
tolerance in the art, for example within 2 standard deviations of
the mean. "About" can be understood as within 10%, 9%, 8%, 7%, 6%,
5%, 4%, 3%, 2%, 1%, 0.5%, 0.1%, 0.05%, or 0.01% of the stated
value. Unless otherwise clear from the context, all numerical
values provided heroin arc modified by the term "about."
[0028] In exemplary embodiments of the present disclosure disclosed
in the specification, specific structural and functional
descriptions arc merely illustrated for the purpose of illustrating
embodiments of the invention and exemplary embodiments of the
present disclosure may be embodied in many forms and are not
limited to the exemplary embodiments set forth heroin. Exemplary
embodiments of the present disclosure may be variously changed and
embodied in various forms, in which illustrative embodiments of the
invention arc shown. However, exemplary embodiments of the present
disclosure should not be construed as being limited to the
embodiments set forth herein and any changes, equivalents or
alternatives which are within the spirit and scope of the present
disclosure should be understood as falling within the scope of the
invention.
[0029] It will be understood that although the terms first, second,
third etc. may be used herein to describe various elements, these
elements should not be limited by these terms. These terms are only
used to distinguish one element from another element. For example,
a first element may be termed a second element and a second element
may be termed a first element without departing from the teachings
of the present disclosure. It will be understood that when an
element, such as a layer, a region, or a substrate, is referred to
as being "on", "connected to" or "coupled to" another element, it
may be directly on, connected or coupled to the other clement or
intervening elements may be present. In contrast, when an element
is referred to as being "directly on," "directly connected to" or
"directly coupled to" another element or layer, there arc no
intervening elements or layers present. Other words used to
describe the relationship between elements or layers should be
interpreted in a like fashion, e.g., "between," versus "directly
between," "adjacent," versus "directly adjacent," etc. The terms
used in the present specification are used for explaining a
specific exemplary embodiment, not limiting the present inventive
concept.
[0030] Unless otherwise defined, all terms including technical and
scientific terms used herein have the same meaning as commonly
understood by one of ordinary skill in the art to which this
inventive concept pertains. It will be further understood that
terms, such as those defined in commonly used dictionaries, should
be interpreted as having a meaning that is consistent with their
meaning in the context of the relevant art and will not be
interpreted in an idealized or overly formal sense unless expressly
so defined herein. Reference will now be made in detail to the
exemplary embodiments, examples of which are illustrated in the
accompanying drawings. In the drawings the same reference numerals
in the drawings denote the same element.
[0031] FIG. 1 is a diagram showing a performance reduction rate and
a platinum (Pt) charge quantity reduction rate depending on an
operating voltage range of a cell included in a fuel cell stack.
Referring to FIG. 1, in general, the fuel cell stack is formed by
stacking a plurality of unit cells in series. The performance
reduction rate and the Pt charge quantity reduction rate, which are
characteristics of a catalyst included in a membrane electrode
assembly (MEA), may be changed based on the operating voltage range
between upper and lower voltage limits of the cell included in the
fuel cell stack.
[0032] In particular, as seen from an operating voltage range
{circle around (1)} or the first range) between about 0.95 V and
0.6 V, which corresponds to when upper and lower voltage limits of
a cell voltage are not adjusted separately, the performance
reduction rate and the Pt charge quantity reduction rate are high.
As seen from an operating voltage range {circle around (2)} or the
second range) between about 0.85 V and 0.6 V. which corresponds to
the operating voltage range of a general fuel cell vehicle, the
performance reduction rate is reduced by half or less.
[0033] As seen from operating voltage ranges {circle around (1)},
{circle around (2)}, {circle around (3)}, {circle around (4)}, and
{circle around (5)} or the first through fifth range), when the
upper voltage limit is gradually reduced, the performance reduction
rate may be gradually reduced. However, as shown in FIG. 1,
compared with the operating voltage ranges {circle around (4)} and
{circle around (5)}, the performance reduction rate is changed
minimally due to the reduction in the upper voltage limit, and
thus, the effect of increasing durability is negligible. However,
as seen from the operating voltage ranges {circle around (4)},
{circle around (1)}, and {circle around (6)} , when the lower
voltage limit is increased, the performance reduction rate and the
Pt charge quantity reduction rate arc reduced. In other words, as
seen from the operating voltage range {circle around (6)} between
0.8 V and 0.75 V, durability is the highest
[0034] In a fuel cell system according to the related art, it is
difficult to restrict the operating voltage of a fuel cell stack
due to the limitations of a high-voltage battery. In particular,
when the voltage of the fuel cell stack is restricted to an upper
voltage limit or less, surplus power generated in the fuel cell
stack needs to be charged in the high-voltage battery, and when the
voltage of the fuel cell stack is restricted to a lower voltage
limit or greater, the power output from the fuel cell stack is
restricted, and thus, power needs to be additionally discharged
from the high-voltage battery.
[0035] However, there is a limit in restricting the voltage of the
fuel cell stack due to limitations on the charge and discharge
power of a battery and the capacitance of a buttery, and thus,
conventionally, there is a problem in that a fuel cell is
controlled to be operated with an upper voltage of only 0.85 V.
However, a commercial vehicle such as a bus, a truck, or a train
requires an operating time period such that a fuel cell stack lasts
three to five times as long as that of a passenger vehicle before
reaching an end of life (EOL), and thus further ensuring the
durability of the fuel cell stack may be particularly required.
Since a commercial vehicle has a low limit in a space or a weight
of a high-voltage battery compared with a passenger vehicle, a
high-voltage battery with high capacitance may be installed in lie
commercial vehicle in order to enhance the durability of the fuel
cell stack.
[0036] FIG. 2 is a diagram showing tire configuration of an
operation control system of a fuel cell according to an exemplary
embodiment of the present disclosure. Referring to FIG. 2, the
operation control system of the fuel cell according to an exemplary
embodiment of the present disclosure may include a fuel cell stack
10, a motor 30 connected to the fuel cell stack 10 via a main bus
end 20 to receive power, a booster 21 disposed between a load and
the fuel cell stack 10 of the main bus end 20 to adjust the output
voltage of the fuel cell stack 10, a high-voltage battery 40
connected between a load and the booster 21 of the main bus end 20,
a voltage sensor 60 connected between the booster 21 and the fuel
cell stack 10 of the main bus end 20 to measure an output voltage
of the fuel cell stack 10, and a voltage controller 50 configured
to set an upper or lower voltage limit of the fuel cell stack 10
based on the state of the fuel cell stack 10 or the high-voltage
battery 40 and operate the booster 21 to maintain the output
voltage of the fuel cell stack 10, measured by the voltage sensor
60, at the set upper voltage limit or less or the lower voltage
limit or greater.
[0037] Moreover, hydrogen and air may be supplied to the fuel cell
stack 10, and electric energy may be generated via a chemical
reaction therein. Power generated by the fuel cell stack 10 may be
supplied to the motor 30 connected thereto via the main bus end 20.
The voltage sensor 60 configured to measure the output voltage of
the fuel cell stack 10 may be disposed at the main bus end 20
connected to an output end of the fuel cell stack 10. The booster
21 may correspond to a direct current (DC) booster and may be
disposed between the fuel cell stack 10 and the motor 30 to convert
and adjust the voltage output from the fuel cell stack 10. The
voltage of the fuel cell stack 10 may be increased using the
booster 21, and thus, even when the voltage of the fuel cell stack
10 is maintained, it may be possible to operate the fuel cell at a
voltage at which an inverter 31 or the like for driving the motor
30 is normally operated.
[0038] The motor 30 may be connected to the fuel cell stack 10 and
the main bus end 20 to receive power. The main bus end 20 may also
be connected to the high-voltage battery 40 to supply power to the
motor 30 via discharging. A balance of plant (BOP) 80 may
correspond to auxiliary devices for power generation of the fuel
cell stack 10 and may be connected to the main bus end 20 to
receive power. The BOP 80 may be connected between the fuel cell
stack 10 and the booster 21.
[0039] As described below, the high-voltage battery 40 may be a
high-voltage battery with high capacitance, formed by increasing
maximum dischargeable power, maximum chargeable power, and energy
capacitance. The high-voltage battery 40 may be charged with power
generated by the fuel cell stack 10 or may supplement the power of
the fuel cell stack 10 and may be discharged to supply power to the
motor 30.
[0040] Depending on the voltage range of the high-voltage battery
40, a bidirectional converter 41 configured to adjust an output
voltage of a high-voltage battery may be included in the
high-voltage battery 40, or may be omitted. The voltage controller
50 may a component within a fuel cell vehicle control unit (FCU),
such as an electronic control unit (ECU), or may be a low level
controller of the FCU. The voltage controller 50 may be configured
to operate the booster 21 to maintain the output voltage of the
fuel cell stack 10, measured by the voltage sensor 60, at the set
upper voltage limit or less or the lower voltage limit or greater.
In particular, as described below, the upper voltage limit and the
lower voltage limit may be set based on the state of the fuel cell
stack 10 or the high-voltage battery 40.
[0041] Accordingly, since the voltage of the fuel cell stack 10 may
be adjusted to be within the range of the upper voltage limit or
less and the lower voltage limit or greater using the booster 21,
the operating voltage range of the fuel cell stack 10 may be
restricted to minimize a change in a physical condition such as a
temperature or pressure of the fuel cell stack 10, and the fuel
cell stack 10 may be prevented from being exposed to high potential
to thus prevent degradation of a catalyst, thereby achieving an
effect of enhancing the durability of the fuel cell stack 10.
[0042] In particular, the voltage controller 50 may be configured
to operate the booster 21 to charge the high-voltage battery 40
while increasing the output current of the fuel cell stack 10 when
the output voltage of the fuel cell stack 10 is equal to or greater
than the set upper voltage limit. In other words, when the power
required to be output from the fuel cell stack 10 is reduced and
the output voltage of the fuel cell stack 10 is increased, the
output voltage of the fuel cell stack 10 may be prevented from
being increased, using the booster 21, and thus, output current of
the fuel cell stack 10 may be generated to charge the high-voltage
battery 40.
[0043] On the other hand, the voltage controller 50 may be
configured to operate the booster 21 to discharge the high-voltage
battery 40 while maintaining the output voltage of the fuel cell
stack 10 when the output voltage of the fuel cell stack 10 is equal
to or less than the set lower voltage limit. In other words, when
the power required to be output from the fuel cell stack 10 is
increased and the output voltage of the fuel cell stack 10 is
reduced, the output voltage of the fuel cell stack 10 may be
prevailed from being reduced, using the booster 21, and thus the
power required by the motor 30 may be discharged from the
high-voltage battery 40 and may be supplied to the motor 30.
[0044] Accordingly, the fuel cell may be operated to prevent the
operating voltage range of the fuel cell stack 10 from being beyond
or outside of the range between the upper and lower voltage limits.
Thus, chargeable power of the high-voltage battery 40 needs to be
at a level of excess power of the fuel cell stack 10, and
dischargeable power of the high-voltage battery 40 needs to be at a
level of insufficient power for the power required by the motor 30
due to limitations of the lower voltage limit of the fuel cell
stack 10. In addition, stored electric energy needs to be
sufficient to continuously perform such charging and discharging
for a substantial period of time.
[0045] In particular, the maximum dischargeable power of the
high-voltage battery 40 may be about 70% or greater of the maximum
power to be consumed by the motor 30. In other words, the
high-voltage battery 40 may be discharged with about 70% or greater
of the maximum power, which is the maximum value of power consumed
by the motor 30. Accordingly, since the output voltage of the fuel
cell stack 10 may be prevented from being decreased to the lower
voltage limit or less, the high-voltage battery 40 may be
configured to supply power to sufficiently compensate for
insufficient power for power required by the motor 30, which is
output from the fuel cell stack 10.
[0046] The maximum chargeable power of the high-voltage battery 40
may be about 70% or greater of the maximum power to be output by
the fuel cell stack 10. Since the output voltage of the fuel cell
stack 10 may be prevented from being increased to the upper voltage
limit or greater, excess power, among the power output from the
fuel cell stack 10, may be charged in the high-voltage battery 40.
In addition, the energy capacitance of the high-voltage battery 40
may be equal to or greater than electric energy of the motor 30,
which is required to drive a vehicle for about 20 km. In other
words, maximum dischargeable electric energy from the state in
which the high-voltage battery 40 is completely charged to the
state in which the high-voltage battery 40 is completely discharged
may be used to drive the motor 30 using only the high-voltage
battery 40 to drive a fuel cell vehicle for an average of about 20
km or greater. The electric energy of the motor 30 required to
drive a vehicle for about 20 km may be calculated based on average
fuel efficiency (fuel cost). Accordingly, the high-voltage battery
40 may maintain charge or discharge for a substantial period of
lime according to control at an upper or lower voltage limit of the
fuel cell stack 10.
[0047] The operation control system of the fuel cell may further
include a relay 70 disposed between the booster 21 and the fuel
cell stack 10 of the main bus end 20, and a relay controller 71
configured to turn the relay 70 on or off. The relay controller 71
may be configured to block the relay 70 when the fuel cell stack 10
enters a fud cell (FC) stop mode and adjustment of the voltage of
the fuel cell stack 10 is not required.
[0048] FIG. 3 is a diagram showing upper and lower voltage limits
corresponding to the state of the fuel cell stack 10 or the
high-voltage battery 40 according to an exemplary embodiment of the
present disclosure. Further referring to FIG. 3, the voltage
controller 50 may be configured to set an upper or lower voltage
limit of the fuel cell stack 10 based on the state of the fuel cell
stack 10 or the high-voltage battery 40. The relationship between
the output voltage and output current of tire fuel cell stack 10
corresponds to the performance curve shown in FIG. 3, and power
(energy) output from a fuel cell is a product of the output voltage
and the output current. The power (energy) output from the fuel
cell may be varied as the output voltage is varied (I1*V1, I2*V2,
I3*V3, I4*V4).
[0049] In particular, when the fuel cell stack 10 generates power
normally, the voltage controller 50 may be configured to set a
first voltage V2 and a second voltage V3, which are respectively
preset to a maximum voltage and a minimum voltage of an operating
voltage range, in which the durability of the fuel cell stack 10
may be optimized, to the upper voltage limit and the lower voltage
limit, respectively. In other words, when the fuel cell stack 10 is
in a normal power generation state and chargeable and dischargeable
power of the high-voltage battery 40 are within normal ranges, the
booster 21 may be operated to operate tire fuel cell stack 10
between the first voltage V2 and the second voltage V3, which is
preset to an operating voltage range within which the durability of
the fuel cell stack 10 may be optimized. Here, the normal power
generation state means a state in which the fuel cell stack is
driven to generate to follow the power required for the fuel cell
stack, and thereby a state in which power generation of the fuel
cell stack is not stopped or restricted by a separate condition
(temperature, deterioration, etc.).
[0050] The first voltage V2 may be at a level of about 0.8 V based
on the voltage of a unit cell, which is an optimized maximum
voltage in terms of the durability of the fuel cell stack 10. The
second voltage V3 may be at a level of about 0.75 V based on the
voltage of a unit cell as a minimum voltage of a preset period in
such a way that a physical condition is varied minimally in terms
of the durability of the fuel cell stack 10. Accordingly, when the
fuel cell stack 10 is in a normal power generation state, the fuel
cell stack 10 may be operated within a narrow operating voltage
range to minimize a change in a physical condition of a membrane
electrode assembly (MEA), thereby achieving an effect of enhancing
durability.
[0051] When a temperature of the fuel cell stack 10 is estimated to
be a predetermined temperature or less, the voltage controller 50
may be configured to set the lower voltage limit to a third voltage
V4, which is lower titan the second voltage V3 and preset to an
allowable minimum voltage of the fuel cell stack 10. Similar to a
cold starting condition, when a temperature of the fuel cell stack
10 is estimated as a preset temperature or less, the temperature of
the fuel cell stack 10 may be determined to require to be
increased. The preset temperature may be 0.degree. C. or water
freezing temperature. Particularly, when a temperature of a coolant
at an outlet of the fuel cell stack 10 is equal to or less than
0.degree. C. the fuel cell stack 10 may be operated to increase a
temperature.
[0052] When a temperature of the fuel cell stack 10 is increased
during an operation of the fuel cell stack 10, the fuel cell stack
10 may be operated to maintain an output voltage of the fuel cell
stack 10 to be relatively low to accelerate the temperature
increase of the fuel cell stack 10. In particular, when the
temperature of the fuel cell stack 10 is increased during an
operation of the fuel cell stack 10, output performance of the fuel
cell stack 10 may be degraded compared with a normal state, and
thus, the lower voltage limit may be set to the third voltage V4
that is less than the second voltage V3.
[0053] The third voltage V4 may be an allowable minimum voltage of
the fuel cell stack 10 and may be preset in consideration of a
rated voltage of the motor 30 that receives power output from the
fuel cell stack 10 or other balance of plants (BOPs) 80, which
receives power output from the fuel cell stack 10. The third
voltage V4 may be a voltage at which power output from the fuel
cell stack 10 is a highest and may be at a level of about 0.6 V
based on the voltage of a unit cell.
[0054] In addition, when the temperature of the fuel cell stack 10
is increased during an operation of the fuel cell stack 10, the
voltage controller 50 may be configured to set the upper voltage
limit of the fuel cell stack 10 to the second voltage V3. In other
words, the upper voltage limit of the fuel cell stack 10 may also
be decreased to increase thermal energy generated from the fuel
cell stack 10. Accordingly, the temperature increase of the fuel
cell stack 10 may be accelerated and power generated while the
temperature of the fuel cell stack 10 is increased during an
operation of the fuel cell stack 10 may be charged in the
high-voltage battery 40, thereby achieving an effect for a
temperature increase without energy loss.
[0055] When the sum of power output from the fuel cell stack 10 and
dischargeable power of the high-voltage battery 40 is less than the
power required by the motor 30 and when the output voltage is the
second voltage V3, the voltage controller 50 may he configured to
set the lower voltage limit to the third voltage V4, which is less
than the second voltage V3 and preset to an allowable minimum
voltage of the fuel cell stack 10. In particular, the fuel cell
stack 10 is in a normal power generation state, but when
dischargeable power of the high-voltage battery 40 is decreased due
to consumption of electric energy stored in the high-voltage
battery 40, or overheating or cooling of the high-voltage battery
40, the lower voltage limit may be decreased.
[0056] When the sum of power output from the fuel cell stack 10 and
the dischargeable power of the high-voltage battery 40 is less than
the power required by the motor 30 and when the dischargeable power
of the high-voltage battery 40 is reduced and the output voltage is
the second voltage V3, the voltage controller 50 may be configured
to set the lower voltage limit to the third voltage V4, which is
preset to an allowable minimum voltage of the fuel cell stack 10.
Accordingly, the voltage of the fuel cell stack 10 may be decreased
to achieve an effect of satisfying the power required by the motor
30.
[0057] When the fuel cell stack 10 enters a FC stop mode, the
voltage controller 50 may be configured to set the first voltage
V2, which is preset to a maximum voltage of a voltage range in
which the durability of the fuel cell stack 10 is maximized, to the
upper voltage limit, and maybe configured to set the third voltage
V4, which is preset to the allowable minimum voltage of the fuel
cell stack 10, to the lower voltage limit. In the FC stop mode of
the fuel cell stack 10, when the state of charge (SOC) of the
high-voltage battery 40 is equal to or greater than a preset SOC
and the power required by the motor 30 is equal to or less than the
dischargeable power of the high-voltage battery 40, power
generation of the fuel cell stack 10 may stopped and the motor 30
may be driven only by the power discharged from the high-voltage
battery 40. In the FC stop mode of the fuel cell stack 10, air
supply to the fuel cell stack 10 may be blocked and concentration
adjustment of hydrogen may be stopped.
[0058] In the early stage in which the fuel cell stack 10 enters
the FC stop mode, the hydrogen and oxygen already supplied to the
fuel cell stack 10 remains within the stack, and thus, the output
voltage of the fuel cell stack 10 requires continuous adjustment.
Particularly, the current state is the state in which the voltage
of the fuel cell stack 10 is decreased, and thus, the lower voltage
limit may be set to the third voltage V4, which is preset to the
allowable minimum voltage of the fuel cell stack 10.
[0059] When the voltage of the fuel cell stack 10 is reduced to the
third voltage V4 or less, the voltage controller 50 may be
configured to stop adjustment of the voltage of the fuel cell stack
10 using the booster 21. In particular, the operation control
system of the fuel cell may further include the relay 70 disposed
between the booster 21 and the fuel cell stack 10 of the main bus
end 20, and the relay controller 71 configured to turn the relay 70
on or off. The relay controller 71 may be configured to block the
relay 70 when the fuel cell stack 10 enters a FC stop mode and the
voltage of the fuel cell stack 10 is reduced to the third voltage
V4 or less.
[0060] In other words, when the fuel cell stack 10 enters the FC
stop mode and the output voltage is reduced to the third voltage V4
or less, oxygen remaining in the fuel cell stack 10 may be entirely
consumed and air may not be supplied any longer, and thus, power
generation of the fuel cell stack 10 may be stopped. The relay 70
may be operated to interrupt the connection between the fuel cell
stack 10 and the booster 21 and thus, the voltage of the fuel cell
stack 10 may be prevented from increasing to the open circuit
voltage (OCV).
[0061] The voltage of the fuel cell stack 10 may be consumed by
charging the high-voltage battery 40, and then, the relay 70 may be
blocked. When the relay controller 71 blocks the relay 70 while a
significant amount of current flows in the main bus end 20, the
relay 70 may be melting-adhered and be damaged. Accordingly, when
the voltage of the fuel cell stack 10 is reduced to the third
voltage V4 or less and the current flowing in the main bus end 20
is reduced to a stable range or lower, the relay controller 71 may
be configured to block the relay 70.
[0062] When the fuel cell stack 10 is released from the FC stop
mode, the voltage controller 50 may be configured to set a fourth
voltage V1, which is preset to a maximum voltage for the durability
of the fuel cell stack 10, to the upper voltage limit. When the
electric energy charged in the high-voltage battery 40 is again
reduced to restart power generation by the fuel cell stack 10,
sufficient concentration of hydrogen supplied to the fuel cell
stack 10 needs to be ensured to generate power normally in the fuel
cell stack 10. In other words, when it is difficult to immediately
permit a load of the motor 30, on excessive amount of current may
be prevented from being generated while preventing the fuel cell
stack 10 from being exposed to the OCV. Accordingly, the upper
voltage limit of the fuel cell stack 10 may be increased to the
fourth voltage V1 to alleviate the problem. The fourth voltage V1
may be at a level of about 0.85 V based on the voltage of a unit
cell, which is an allowable maximum voltage, to prevent the
durability of the fuel cell stack 10 from being degraded.
[0063] Accordingly, until live fuel cell stack 10 is restored to a
normal power generation state, the fuel cell stack 10 may be
operated to prevent the load of the motor 30 from being excessive
and to prevent the fuel cell stack 10 from being exposed to a high
voltage close to OCV. When an internal suite (e.g., output voltage,
hydrogen concentration, etc.) of the fuel cell stack 10 is normally
restored, the fuel cell stack 10 may be restored to a normal
driving mode.
[0064] FIG. 4 is a flowchart of an operation control method of a
fuel cell according to an exemplary embodiment of the present
disclosure. The method described herein below may be executed by a
controller having a processor and memory. The controller may be
specifically programmed to execute the method. Referring to FIG. 4,
the operation control method of the fuel cell may include
determining the state of a fuel cell stack or a high-voltage
battery (S100), setting an upper or lower voltage limit of the fuel
cell stack based on the determined state of the fuel cell stack or
the high-voltage battery (S200), and operating a booster disposed
at a main bus end for connection between the fuel cell stack and a
motor to maintain an output voltage of the fuel cell stack to the
set upper voltage limit or less or the lower voltage limit or
greater (S300).
[0065] In the determining of the state of the stack (S100), in
response to determining the state to be the state in which the fuel
cell stack generates power normally, a first voltage and a second
voltage, which arc respectively preset to a maximum voltage and a
minimum voltage of a voltage period in which the durability of the
fuel cell stack is optimized, may be set to the upper voltage limit
and the lower voltage limit, respectively (S260) in the selling of
the upper voltage limit or the lower voltage limit (S200).
[0066] In the determining of the state of the stack (S100), in
response to determining that a temperature of the fuel cell stack
is equal to or less than a preset temperature (S140), the lower
voltage limit may be set to a third voltage, which is less than the
second voltage and is preset to an allowable minimum voltage of the
fuel cell stack (S240) in the setting of the upper voltage limit or
the lower voltage limit (S200). Additionally, when the sum of power
output from the fuel cell stack and dischargeable power of the
high-voltage battery is less than power required by a motor in the
state in which the output voltage is the second voltage (S150), the
lower voltage limit may be set to the third voltage, which is less
than the second voltage and is preset to an allowable minimum
voltage of the fuel cell stack (S250) in the setting of the upper
voltage limit or the lower voltage limit (S200).
[0067] In response to determining that the fuel cell stack enters a
fuel cell (PC) stop mode (S110), the first voltage that is preset
to a maximum voltage of a voltage range in which the durability of
the fuel cell stack is optimized, may be set to the upper voltage
limit, and the third voltage, which is preset to an allowable
minimum voltage of the fuel cell stack, may be set to the lower
voltage limit (S210) in lire setting of the upper voltage limit or
the lower voltage limit (S200).
[0068] Further, in the operating of the booster (S300), when the
voltage of the fuel cell stack is reduced to the third voltage or
less (S120), adjustment of the voltage of the fuel cell stack using
the booster may be stopped (S300'). Additionally, when control of
the voltage of the fuel cell stack is stopped (S300'), the method
may further include blocking a relay disposed at a main bus end
between the fuel cell stack and the booster (S400) after the
operating of the booster (S300). In the determining of the state of
the stack (S100), in response to determining that the fuel cell
stack is released from a FC stop mode (S130), a fourth voltage,
which is preset to an maximum voltage for the durability of the
fuel cell stack, may be set to the upper voltage limit (S230) in
the setting of the upper voltage limit or the lower voltage limit
(S200). The lower voltage limit may be set to the third voltage,
which is preset to an allowable minimum voltage of the fuel cell
stack.
[0069] As described above, a system and method of controlling an
operation of a fuel cell according to the present disclosure may
prevent a fuel cell stack from reaching a high voltage, thereby
achieving an effect of substantially increasing the durability of a
fuel cell stack. In addition, since an operation voltage range of a
fuel cell stack is reduced, a change in a physical condition of the
fuel cell stack may be minimized, thereby achieving an effect of
enhancing the durability of the fuel cell stack.
[0070] Accordingly, the aforementioned exemplary embodiments are
exemplary in all aspects and are understood not to be limited. The
scope of the present disclosure is defined by the following claims
but not the above description and the meaning and scope of the
claims and all modifications or modified forms from equivalents
thereof are within tire scope of the present disclosure.
* * * * *